1. Field of Endeavor
The invention refers to a seal and sealing arrangement for stemming leakage flows between adjacent components of turbomachines, especially gas turbines, wherein the seal has an elongated, thin-walled sealing element which is elastically deformable in at least one transverse direction and which, in cross section, has the shape of a bent band.
2. Brief Description of the Related Art
In the installed state, the seal is arranged in a space, which is delimited by walls of the two components, in a pretensioned manner in at least one transverse direction in such a way that the at least one transverse direction extends perpendicularly to two oppositely disposed sealing surfaces, of which one is on a wall of the one component and the other is on a wall of the other component.
Such a seal and sealing arrangement are known from EP 1 378 690 A2. In the case of this seal, which is arranged in an open space which is delimited by two parallel sealing surfaces and a supporting wall which perpendicularly adjoins one of the sealing surfaces, the space being part of a gap which separates the two components from each other, the sealing element can have various cross-sectional shapes, of which one corresponds to a “C” (FIG. 3), another resembles a “U” in a center section (FIGS. 1, 2), adjoining the legs of which are two outwardly bent, round sections, and a further shape resembles an “E” (FIG. 4). Both in the case of the sealing element which is C-shaped in cross section and in the case of the sealing element which is E-shaped in cross section, an opening, which faces a high-pressure side of the gap, is located between the free ends in each case. There is an opening which faces the high-pressure side of the gap also in the case of the sealing element with a cross section which is U-shaped in the center section. This opening is located between the two outwardly bent, round end sections of the sealing element. Common to all the aforesaid cross-sectional shapes of the sealing element of the known seal is that in each case they have two contact regions, which bear against the sealing surfaces of the components, in the proximity of the free ends of the sealing element and also have a supporting region which bears against the supporting wall, wherein the supporting region is exposed to the low-pressure side of the gap.
The sealing element of the known seal is arranged in the space between the two components in a pretensioned manner so that, in the case of a, for example, thermally induced widening of the gap perpendicular to the oppositely disposed sealing surfaces, the sealing element is deformed in such a way that the respective opening is widened and the contact regions of the sealing element follow the sealing surfaces—which move away from each other—of the components. On the other hand, if in the case of a, for example, also thermally induced narrowing of the gap perpendicular to the oppositely disposed sealing surfaces, the sealing element is deformed in such a way that the respective opening is narrowed and the distance between the contact regions which bear against the sealing surfaces is reduced.
Since the opening of the sealing element of the known seal faces the high-pressure side of the gap and a surface section of the sealing element, which includes the supporting region, is exposed to the low-pressure side of the gap, forces result from the pressure difference, acting on the sealing element, which on the one hand increase the spring forces which arise as a result of elastic deformation of the sealing element and press the contact regions against the sealing surfaces of the construction elements, and on the other hand tightly press the supporting region against the supporting wall. The forces which result from the pressure difference between the high-pressure side and the low-pressure side of the gap act upon the contact regions of the sealing element in the same direction as the spring forces which arise as a result of elastic deformation of the sealing element. Consequently, the contact regions of the sealing element are also pressed against the sealing surfaces of the components if the spring forces are no longer effective as a result of excessively large gap-widening or material fatigue of the sealing element as a consequence of constantly changing deformation of the sealing element. Contingent upon the respective cross-sectional shape of the sealing element of the known seal, tight limits are set, however, to the elastic deformability of the sealing element so that they can only bridge such gaps which widen only a little in comparison to an initial gap width.
Whereas the sealing element—which is C-shaped in cross section, is U-shaped in the center section, or resembles an “E”—of the known seal maintains its sealing action in the case of a change of the relative position of the components perpendicular to its sealing surfaces which is not excessive, a neutralization of the sealing effect of the sealing element can occur if the components alter their relative position parallel to its sealing surface. In the case of such a relative change of position of the components, in particular the frictional resistance which acts between the contact regions of the sealing element and the sealing surfaces contributes to the sealing element being pressed more tightly against the supporting wall, depending on the direction of movement of the components, as a result of which a skewing of the sealing element is the consequence, or the sealing element is moved away from the supporting wall, as a result of which a change of position of the sealing element relative to the components is the consequence. Both consequences—skewing and change of position of the sealing element—have a disadvantageous effect on the sealing capacity of the known seal.
In order to reduce the frictional resistance between the sealing element and the components so that the sealing element, in the case of a relative change of position of the components parallel to its sealing surfaces, is less strongly inclined to skewing or to a change of position relative to the components, provision is made in a further embodiment (FIG. 5) of the known seal for welding or soldering two contact bodies onto the sealing element which is C-shaped in cross section, which contact bodies in their turn carry contact regions which bear against the sealing surfaces of the components. By using suitable materials for the contact bodies and for the sealing element which is C-shaped in cross section, the sealing surfaces of the components can slide along the contact regions of the contact bodies if the components move relative to each other parallel to their sealing surfaces without impairing the sealing performance, while at the same time the sealing element which is C-shaped in cross section furthermore has good elastic properties.
However, even this multipiece embodiment of the known seal cannot bridge larger gaps than the aforementioned one-piece embodiments of the known seal.
A seal with a one-piece sealing element, the cross-sectional shape of which consists of a U-shaped center section and two end sections which adjoin the U-shaped center section and are outwardly bent round, is also known from EP 1 323 894 A2. This known seal is arranged in a groove which is U-shaped in cross section which is arranged in one of two contiguous components of a gas turbine. The sealing element bears by a supporting region, which is located on the outer side of the U-shaped center section, against a supporting wall which is one of two oppositely disposed walls of the U-shaped component groove. The components have two oppositely disposed sealing surfaces, of which one is located on the bottom of the U-shaped groove. The sealing element is arranged in a pretensioned manner in a space between the two components so that the bent-round end sections bear by their respective outer side against the oppositely disposed sealing surfaces of the components. The wall of the U-shaped component groove which lies opposite the supporting wall has a substantial distance from the bent end sections of the sealing element. Consequently, the sealing element can move between the two oppositely disposed walls of the groove which is U-shaped in cross section by a degree which can lead to skewing of the sealing element if the components move correspondingly. Neither is this seal suitable for maintaining its sealing performance if a larger gap develops between the two components because the end sections of the sealing element then no longer bear, or do not bear tightly enough, against the sealing surfaces of the components.
From U.S. Pat. No. 4,854,600 A, a seal which is exposed to a pressure difference with an annular sealing element is known, which sealing element in cross section has the shape of a repeatedly bent band which has a plurality of consecutive bends with alternating bend directions, where each bend is the cross-sectional shape of an associated bent wall section of the sealing element. In one embodiment (FIGS. 1, 8, 9, 10), the sealing element has an “S” shape in cross section, in which it has two consecutive, oppositely bent wall sections which are interconnected by a wall section which extends transversely to the direction of movement. An end section, which has the respective free end, adjoins each of the bent wall sections and has a bend in each case, the convex outer side of which bears against a sealing surface of the respective component. The seal is arranged in a pretensioned manner in an annular space between two concentrically arranged components, wherein the two sealing surfaces of the components are oriented pointing either axially or radially. The sealing element is elastically deformable perpendicularly to the sealing surfaces, wherein it is elastically deformable to a greater extent in this direction than, for example, a sealing element which is C-shaped in cross section, but during movements of the components parallel to its sealing surfaces is exposed to the risk of its position changing, just like a sealing element which is C-shaped in cross section.
In another embodiment (FIGS. 4, 5), the sealing element consists of a section which is S-shaped in cross section and a section which is rectilinear in cross section which is connected to one end of the S-shaped section by welding and serves for preventing the S-shaped section of the annular sealing element from rotating. The rectilinear section is the cross section of a flat ring.
In a further embodiment (FIG. 3), the sealing element has more than two consecutive bent wall sections and has an end section which is rectilinear in cross section and has a convex surface region which bears against a sealing surface of the associated component. This embodiment has a high elastic deformability perpendicular to the parallel sealing surfaces of the components. Consequently, this embodiment can be used where greater movements of the components perpendicular to its sealing surfaces are to be expected. However, this embodiment of the known seal is also unfavorably loaded during a movement of the components parallel to its sealing surfaces so that as a result of such movements an undesirable skewing or change of position of the sealing element can occur with disadvantageous effects upon the sealing performance.
An annular seal is known from U.S. Pat. No. 5,630,593 A, in which the elastically deformable sealing element can be single-layered or multilayered and is either U-shaped in cross section with outwards bent-round end sections (FIGS. 2, 3, 4) or is E-shaped (FIGS. 6, 10) with three consecutive bent wall sections and two end sections which are bent round outwards. The sealing element can be exposed to a pressure difference in such a way that the outwards bent-round end sections are pressed more strongly against the oppositely disposed sealing surfaces of the components. The multilayered construction has a higher rigidity than the single-layered construction. In one of the material layers of the sealing element, provision may be made for slots which are spaced apart in the circumferential direction, in order to increase the flexibility of the sealing element. This seal is suitable for bridging gaps which vary relatively little in their width between two components. The sealing performance of this known seal, however, is also put at risk if the components move parallel to its sealing surfaces.
Also known from experience are so-called double-E seals which consist of two sealing elements which are E-shaped in cross section, these being interconnected by a cover strip, which is band-like in cross section, by welding or soldering. This type of seal, just like the single sealing element which is E-shaped in cross section, can bridge larger gaps than the sealing element which is C-shaped in cross section. The double-E seal is certainly less susceptible than the single-E seal to skewing or to displacement during relative movements of the components oriented parallel to the sealing surfaces. Larger relative movements of the components parallel to its sealing surfaces, however, also impair the positional stability and resistance to wear of the double-E seal so that, during larger relative movements of the components parallel to its sealing surfaces, failure of the double-E seal can occur. If the double-E seal, for example, is used where the cooling air plenum is to be sealed against the combustion plenum of gas turbine combustors, leakages into the combustion chamber of the combustor can occur as a result of larger relative movements of the components, which are to be sealed against each other, parallel to its sealing surfaces, as a result of which performance and efficiency losses and also emissions and, in the most serious case, combustion instabilities, may be the consequence. On account of the loss of sealing, premature readjustment of the operating parameters of the gas turbine is then frequently required.